1. Field of the Invention
The present invention relates to a light emitting display device. Particularly, the present invention relates to a light emitting display device that has less size and prevents moisture penetration by installing a driving chip within a cap.
2. Description of the Related Art
A cathode ray tube, one of the display devices, has a drawback that it is heavy and bulky. Recently, various flat display devices with less weight and volume have been developed. Such flat display devices include a liquid crystal display device, a field emission display device, a plasma display panel, and an organic electroluminescent device. Particularly, an organic electroluminescent device has a structure that electrodes are contacted at both surfaces of an organic material layer having a hole transport layer, a luminescent layer, and an electron transport layer, stacked in order. The organic electroluminescent device is now receiving attention as next generation display device due to its wide viewing angle, high aperture rate, and high chromaticity.
Organic electroluminescence is a phenomenon that excitons are formed in an organic (low molecular or high molecular) material thin layer by re-combining holes injected through an anode with electrons injected through a cathode, and a specific wavelength of light is generated by energy from the formed excitons, and thus the organic electroluminescent device can be operated by low voltage. Therefore, the device's power consumption is low, and the device's quality of color is good. Also, the organic electroluminescent device can be formed on a flexible substrate.
FIG. 1 is a plan view of an organic electroluminescent device in the related art. FIG. 2 is a cross-sectional view of the organic electroluminescent device of FIG. 1, as taken along line II-II′
In FIG. 1, the constitution disposed on a substrate 10 within a cap 40 is not illustrated for the convenience of explanation. The area defined by dotted lines means an area applied by sealant 44 and conductive bonding film 54.
Referring to FIGS. 1 and 2, the organic electroluminescent device comprises an active area 12 disposed on the substrate 10, the cap 40 surrounding the active area 12, and a driving chip 60 disposed within the cap 40 to make the active area 12 emit.
The basic structure of the organic electroluminescent device includes the substrate 10, an anode electrode layer 20 formed on the upper side of the glass substrate 10, an organic material layer 24 formed on the anode electrode layer 20, and a cathode electrode layer 22 formed to cross the anode electrode layer 20 on the organic material layer 24. Here, the structure that the anode electrode layer 20, the organic material layer 24, and the cathode electrode layer 22 are stacked in order is defined as a pixel 26. Also, the entire area of the pixels 26 is defined as the active area 12.
The organic material layer 24 has a structure that the hole transport layer, the luminescent layer, and an electron transport layer are stacked in order. Each cathode electrode layer 22 maintains a certain space from adjacent cathode electrode layers 22. The anode electrode layer 20 acts as the anode electrode, and the cathode electrode layer 22 acts as the cathode electrode.
An inner wall 30 partitions two adjacent cathode electrode layers 22. The inner wall 30 is formed in an area between two adjacent cathode electrode layers 22. The inner wall 30 is separated from the anode electrode layer 20 by an insulating layer 28. Although organic material and cathode electrode material are deposited on the upper side or the top of each inner wall 30 during the processes of forming the organic material layer 24 and cathode electrode layer 22, neither functions as a component of the device.
The cap 40 covers the active area 12 on the substrate 10 to prevent it from oxygen and moisture in the air. The cap 40 can be made of glass, and a recessed space is formed in the center of the cap 40 by sand blasting process. Here, the recessed space of the cap 40 has enough height not to contact the elements disposed in the active area 12. Also, a getter 42 is disposed within the cap 40 to absorb oxygen and moisture.
The driving chip 60 is installed within the cap 40. The driving chip 60 generates data signal transferred to the anode electrode layer 20 in the active area 12. The driving chip 60 is electrically communicated with a first flexible printed circuit 62.
As shown in FIG. 1, in the area that the cap 40 is attached to the substrate 10 (the area illustrated by dotted lines), the conductive bonding film 54 is applied to the area which the pad 52 crosses, and the sealant 44 is applied to the remaining area. An anisotrophic conductive film is preferable as the conductive bonding film 54.
External signals (hereinafter, referred to as “external signal”) is transferred from the external device (not shown) to the pad 52 through a second flexible printed circuit 50, and is transferred to the driving chip 60 through the conductive bonding film 54 and the first flexible printed circuit 62. Therefore, the driving chip 60 responds to the external signal to generate data signal and scan signal.
Data signal and scan signal generated from the driving chip 60 is transferred to the active area 12 through the first flexible printed circuit 62, the conductive bonding film 54, and the pad 52. Thus, the pixels 26 in the active area 12 are emitted.
This organic electroluminescent device in the art has drawbacks that the manufacturing process is complicated, and the manufacturing cost is high because the recessed space is formed on the glass cap by sand blasting process. Also, moisture can penetrate more through the area that the cap 40 is attached to the substrate 10 by the conductive bonding film 54 than the area applied by the sealant 44. Therefore, the organic electroluminescent device is degraded by moisture penetration through the area applied by the conductive bonding film 54.